A few days after announcing a $1 million donation to kickstart a new animal foundation, Katherine Heigl is back making headlines after lighting up while appearing on "Letterman". 

Granted, the 31-year-old wasn't actually smoking a tobacco product -- but an alternative called an "e-cigarette". The devices, which have enjoyed rapid popularity since debuting in 2006, let you inhale nicotine while puffing out a cloud of (supposedly) harmless water vapor. 

"You blow out water vapor so you're not harming anyone around you and you're not harming yourself," she said. "I'm essentially humidifying the space."

The actress told Letterman that she's tried for years to quit her nasty smoking habit, but that all of the options she tried just didn't work. "I went bananas," she added before whipping out her smoking stick. 

Of course, while the smoking stick reduces the need for real cigarettes -- providing the nicotine the body craves -- by no means does it necessarily help to break the addiction; a point Letterman was quick to jump on. 

"Now," he asked, "is there a chance you'll become addicted to the device?" "... Oh yeah," the actress replied, "I'm totally addicted to the device." Something tells me that's the manufacturer's plan. 

It should also be noted that the FDA is keeping a close eye on "e-cigarettes", having recently warned that the "harmless" gadgets may potentially be unsafe. No doubt, as they grow in popularity, increased scrutiny will fall on the health claims offered by sellers. 

Check out Heigl lighting up on Letterman below: 

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